However, he admitted to being intrigued about what might be available to him next year when Beauden Barrett rejoins the side.
Tuivasa-Sheck's return to rugby was confirmed on Saturday, but any thoughts about what position he would play were still to happen.
There had been 'minimal dialogue' so far on that aspect, he said.
However, he said there was no doubt the benefits he would provide for the Blues 2022 Super Rugby side.
"He gives us versatility," MacDonald said.
"We know he played his schoolboy rugby in the midfield, we know he's been playing his league in the outsides so, one of the attractions for us is, he's multi-skilled, and he gives us options.
"We'll sit down once he's finished his campaign, and we've finished ours, and work out a plan but what that looks like we're not certain," he said.
MacDonald expected that it was likely, closer to the time he joined rugby, that discussions with the All Blacks selectors would be involved.
He acknowledged that Tuivasa-Sheck was taking a risk leaving a game he was excelling at, and that was something MacDonald admired.
He had the hunger, he had played rugby for a period of his life and was coming to the side to do everything he could to be successful.
"We're excited to have him here, and there is a bit of a buzz around the team as well," he said.
MacDonald said there was much he had been impressed by Tuivasa-Sheck's league career.
Everyone knew he was good on his feet, but he was also tough. He could play at the line, he could put the ball through, he was a good defender and was resilient and he played a lot of minutes, he said.
"There's a lot to like about Roger and the way he plays league and I think he'll transfer over pretty well," he said.
Based on previous experience of code-crossing players, MacDonald said one of the issues for Tuivasa-Sheck would be managing expectations. There would be people who expected him to be world-class in his first game, but that was not likely.
"There has got to be a little bit of empathy from the public to let him relearn the trade…it will take some time to change things around. There's a lot to learn in the game, the game's evolved. There's a lot of structural stuff that probably wasn't there when he last played…it will be like being back at school for the first little while," he said.
It was about playing the game instinctively, and that would take some time, he said.
Chief executive Andrew Hore wasn't prepared to talk about what financial implications there may have been in securing Tuivasa-Sheck's signature. He said it wasn't appropriate to discuss his arrangements or those of any other player. He said it was a three-way arrangement between New Zealand Rugby, the Blues and Auckland.
When he might make the playing switch was still not clear, although his signing with Auckland suggested he would be looking to play in the Mitre 10 Cup later in the year.
Hore said: "What we are clear on, is he has a campaign he needs to finish, and we have a campaign we have to focus on. As that unfolds there will be discussions about the best pathway for his development."
It would be 'optimal' for him to get as much rugby as possible under his belt before Super Rugby next year.
"It's been 10 years [since he made the switch from schoolboy rugby in New Zealand to league], and he's up against some good young kids coming through – the Zarn Sullivans and so forth of this world who have been playing footy for those last 10 years," Hore said.
There were also off-field advantages for the Blues, especially as they look to work on their social development.
"We've got to get things right on the field first, but there needs to be a bigger purpose to who we are.
"Roger has signalled he's very passionate about that. We think having another Pasifika leader in our environment is important. When you mix it with some young people coming through, and recruitment that's been done, we think there's a good cocktail there," he said.
He would work in that area with lock and captain Patrick Tuipulotu, who was part of the 2011 national schoolboy team with Tuivasa-Sheck. All Blacks teammates Ardie Savea and Ngani Laumape were also part of that side.